Transflective display

ABSTRACT

A display unit for a portable electronic device includes a substantially transparent display layer having a front side for displaying information and a rear side, a color filter layer, a reflector, and a lighting system for illuminating the substantially transparent display from the rear side. The reflector is provided on a front side of the color filter layer facing a user, such that reflected light does not have to travel through the color filter layer. When the lighting system is switched on, the display unit operates in an emissive mode, and when the lighting system is switched off, the display unit operates in a reflective and/or transflective mode. The display unit thereby provides two modes of operation that combine peak performance of an emissive display with a transflective ability to be read without backlighting. In this way, a display is provided which has saturated colors and high luminance, and which is still possible to be read in strong sunlight.

RELATED APPLICATIONS

The present application is a 35 U.S.C. §371 national phase applicationof PCT International Application No. PCT/EP2003/012075, having aninternational filing date of Oct. 30, 2003 and claiming priority toEuropean Patent Application No. 02024307.7, filed Nov. 1, 2002, and U.S.Provisional Application No. 60/424,623 filed Nov. 7, 2002, thedisclosures of which are incorporated herein by reference in theirentireties. The above PCT International Application was published in theEnglish language and has International Publication No. WO 2004/040360.

TECHNICAL FIELD

The present invention relates to a display unit, and a portableelectronic device comprising such display units.

BACKGROUND OF THE INVENTION

Today, in the world of portable electronic devices provided withdisplays there is a trend towards color displays. This trend is alsovery much present in the world of mobile communications, where more andmore customers demand portable communcation devices having suchdisplays. Typically such displays are of transparent type beingilluminated by a lighting system, typically by a backlighting system.Examples of displays are different types of LCDs (Liquid CrystalDisplays).

The display should be bright with good contrast. However, the powerconsumption of the lighting system (typically the backlighting) is high,thereby limiting the time the display can be switched on (herein, theterm “switched on” means illuminated) in a portable electronic device.Typically an LCD itself consumes about 0.5 mA in a so-called“standby-mode” and about 80 mA with backlight switched on. Of course,this consumes battery power, hence reducing operating time of theportable electronic device.

Therefore, prior art technology has tried to reduce this problem. Oneway is to provide a colour filter that has an reflector behind forreflective operation. Ambient light then passes the colour filter and isreflected back, once more passing the color filter. However, thissolution implies that reflected light (ambient light) has to travelthrough the color filter. Moreover, the reflector also reduce the areaof the coluor filter during transmission of light, typically from abacklighting system. Since a typical colour filter may absorb more than70% of the light this is often not a most desirable solution. There arealso purely transmissive displays, wherein light is only transmittedfrom backlighting. Such solutions could for instance be found inlap-tops. However, these solutions provides poor out-door performance,hence in strong sun-light it could be hard, or even impossible to seeany information on the display. Therefore, often also this solution doesnot perform well in out door use.

In US-A1-2001/0045560 (Bijsma et al) there is disclosed partly coveringreflective parts of electrodes in a transfiective display with colorfilters, whereby the color point is adjusted.

However, there still exists problems with prior art that have to beovercome, or at least reduced.

SUMMARY OF THE INVENTION

According to an aspect, the present invention seeks to solve the problemof providing a display unit, in particular a colour display unit thatdoes not consume a large amount of power, and that combines peakperformance of an emissive display together with an ability to be readwithout lighting.

According to a preferred embodiment of the invention, this problem issolved by a display unit for a portable electronic device, comprising:

-   -   an essentially transparent display layer having a front side        provided for displaying information, and a rear side,    -   a lighting system for illuminating the transparent display from        the rear side, said lighting system being adapted to be switched        on, or off,    -   wherein when the lighting system is switched on, the display        unit is adapted to operate in an emissive mode, when the        lighting system is switched off, the display unit is adapted to        operate in a reflective or a transfiective mode.

Preferably, the display layer on the rear side is provided with a colorfilter layer having a front side facing the display layer, said frontside being provided with at least one reflector.

Herein, the term “front side” is referred to as any side directly facinga user, even after processing.

Preferably, the reflector(s) covers less than 50% of the total area ofthe rear side of the color filter layer.

Preferably, the reflector(s) covers less than 25% of the total area ofthe front side of the filter layer.

Preferably, the reflector is provided in the center of the front side ofthe filter layer.

Preferably, the reflector(s) is/are provided adjacent to an edge of thefront side of the filter layer.

Preferably, the reflector has rectangular shape.

Preferably, the reflector has circular shape.

Preferably, the reflector is made of particles.

According to another preferred embodiment of the invention, there isprovided a portable electronic device comprising:

-   -   a display unit, comprising:    -   an essentially transparent display layer having a front side        provided for displaying information, and a rear side,    -   a lighting system for illuminating the transparent display from        the rear side, said lighting system being adapted to be switched        on, or off,    -   wherein when the lighting system is switched on, the display is        adapted to operate in an emissive mode, when the lighting system        is switched off, the display is adapted to operate in a        reflective mode.

With the proposed invention, there is excellent emissive (transmissive)mode, legibility is better in out-door usage and legibility remains whenlighting, typically backlighting is switched on, rendering greatemissive performance.

These and other aspects and advantages of the invention will in thefollowing be apparent from and elucidated with reference to theembodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of part of a display unit (a red, green, bluepixel) according to an embodiment of the invention.

FIG. 2 a is a sectional view of a display unit according to anotherembodiment of the invention, illustrating a situation when the lightingsystem is switched off.

FIG. 2 b illustrates the same display unit as illustrated in FIG. 2 a,wherein FIG. 2 b shows a situation when the lighting system is switchedon, i.e. when the display unit operates in emissive mode.

FIGS. 3 a and 3 b illustrate part of a display panel comprising aplurality of display units according to preferred embodiments of theinvention.

FIG. 4 is a portable electronic device in the form of a cellular phoneincluding a display panel.

DETAILED DESCRIPTION OF THE INVENTION

Now is referred to FIG. 1, which is a plan view of part of a displayunit 1 (herein a sub-pixel) according to a first embodiment of theinvention. For purpose of simplicity, the display unit 1 is shownwithout an essentially transparent display layer, which in thisparticular case could be a conventional liquid crystal (LC) layer of aliquid crystal display (LCD). Of course also other types of essentiallytransparent layers that can be employed for presenting information couldbe used without departing from the invention. Since the operation of anLCD is well known from prior art, the operating principle thereof willnot be explained in detail.

The display unit 1 further comprises a reflector 2 provided thereon, inthis embodiment of rectangular shape provided at an upper part of afront side 4a of a color filter layer 4. Herein, the term “color filterlayer” is referred to as a layer of suitable thickness and compositioncomprising a color filter of conventional type. Since such filters arewell known from prior art, the composition of this layer will not bedescribed in more detail.

Preferably, the reflector 2 covers less than 50%, in particular lessthan 25% of the total area of the front side 4 a of the filter layer 4.The area selected depends on performance that is desired. A large areaimplies a larger reflection area for ambient light, but, also reducesemissive (transmissive) performance of the display unit 1, since areafor transmission of light from lighting system is reduced. Therefore, abalance between these requirements has to be taken into account. Toselect area of reflector is obvious for a person skilled in the art toachieve, for instance by experiments, and will therefore not bedescribed in more detail herein.

Herein, only one out of three sub-pixels is shown because of simplicity.Typically, a color display pixel contains three sub-pixels, one for eachcolor (red, green and blue). This will not be further described, sinceit is conventional technique for color display pixels. It is also knownthat each pixel (sub-pixel) can be able to have a reflective and aemissive mode of operation. Herein, the term “reflective mode” means amode of operation using reflected light from ambient light, and the term“emissive mode” means a mode of operation using transmitted light from alighting system, typically from a backlighting system. The term“emissive” does not only relate only to a pure emissive operation, butalso to almost a pure one. Both of these operating modes will be furtherexplained below, when describing the operation of the display unitaccording to different embodiments of the invention.

Furthermore, because of simplicity, in this figure, lighting will onlybe schematically described, since a more detailed explanation willfollow below with reference to FIG. 2 a-b. Now, again turning to FIG. 1,it is shown how ambient light light_(amb) is reflected against thereflector 2 (illustrated by two arrows, of which one is incoming and theother is going out from the reflector 2). The reflector 2 can be made ofany suitable type of reflecting material such as metals, for instancealuminium, silver, metal coated polymer material, or the like. Thereflector can also be made from the color filter layer 4 by means ofconventional techniques using masks etc. The material in itself is notessential for the invention, only its function as reflector. The emittedlight_(lightemitted) is illustrated by an arrow going out from the frontside 4 a of the color filter layer 4.

With this solution, the display unit is adapted to operate in anemissive mode, when the lighting system is on, and adapted to operate ina reflective mode when the lighting system is switched off. In emissivemode, the display unit has well defined saturated colors and highluminance. In out door use, they remain, still visible at moderateambient light conditions, whereas, when ambient light becomes veryintense, a typical situation a sunny day outdoors, the display willgradually appear as a grey-scale display, however, which is stillpossible to read. When the lighting system is switched off, the displayoperates in the reflective mode. In this mode, there is no colorinformation, rendering the display to appear as a grey-scale display;however, it can display all information a color display can, but withoutcolors.

For a better understanding of the underlying principle of the inventionand/or reduction to practice, now is referred to FIG. 2 a, which is across-sectional view of a second embodiment of the display unitaccording to the invention, in which embodiment the reflector isprovided in the center of the front side of the filter layer.

In FIG. 2 a, there is shown a display unit 1 comprising a transparentdisplay layer 5, in this case an LC layer having a front side 5 a and arear side 5 b. The front side 5 a is turned to a user 6. Because ofsimplicity, a complete portable electronic device comprising a pluralityof display units is not illustrated in this figure, since the intentionis to explain the operating principle of the invention. Such anelectronic device will be shown below with reference to FIG. 4.

Now, again turning to FIG. 2 a, there is further provided a color filterlayer 4 having a front side 4 a facing the rear side 5 b of thetransparent display layer 5, which front side 4 a is provided with areflector 2 and distances 4 c, in this particular embodiment provided bymeans of a so-called “black mask”. Of course, also other types ofdistances can be employed without departing from the invention.

FIG. 2 a shows the situation when the lighting system is switched offand the display unit 1 operates in the reflective mode (illustrated byan incoming and an outgoing arrow). As is shown, the light will, for theuser 6, appear as reflected light light_(reflected), reflected by thereflector 2. In this embodiment, the reflector 2 is provided in thecenter of the front side 4 a of the color filter layer 4, when seen incross-section, taken in a direction perpendicular to the front side 4 a,as seen by the user 6, of the filter layer 4. This means that only partof the front side 4 a is covered by the reflector 2. Depending on howlarge the area that is covered by the reflector is, reflective/emissiveproperties are changed as explained above. It is important to note thatthe area of the reflector 2 can typically be kept small compared toprior art techniques using color filters provided with metal reflectorson their rear sides, even compared to such a prior art color filterprovided with hole through filter to improve reflection, since reflectedlight does not have to travel through the filter layer by using theprinciple of the invention.

FIG. 2 b shows the same display unit 1 when operating in emissive mode.As is shown, a lighting system 7 is now switched on, whereby light(illustrated by arrows denoted “light_(backlight)”) travel through thecolor filter layer 4 before reaching the user 6. In this case aso-called “back-light” system is shown, illuminating the display layer 4from the rear side 4 b, but also other suitable lighting systems couldbe employed.

The reflector 2 can have rectangular, circular, or have other suitableshape, is not limited to only one reflector, or a particular pattern. Itcan also be provided as flakes, particles or almost any suitable shape.

The transparent display layer 5 can for instance be of conventional LCtype having electrodes of indium tin oxide, enclosed in a glass closure.However, the type of display layer is not essential to the invention,any suitable type could be employed.

Pixel addressing schemes could be of any suitable conventional type,such as row or column addressing schemes, and will therefore not befurther described in more detail. All driving circuits, typicallycomprising timing and control subunits, column drivers and row driversin order to drive an LCD could be designed according to knownprinciples.

Color resolution of the display can be any suitable. When using a higherinput resolution or an embedded gamma function, extra color resolutioncan be exploited.

Further embodiments of the invention will now be described, wherebybecause of simplicity only plan views illustrating the arrangement ofcolor filters and electrode structure will be illustrated.

In FIG. 3 a, part of a display 10 comprising display units 1 accordingto a preferred embodiment of the invention is shown in a plan view. Foursets of display units 1, each set 1 a including three display units 1(i. e. three different color filters 4, one for each color, red, greenand blue) are shown. The color filters can also be combined in strips;however, this is not shown. Each color filter 4 is provided with arectangular reflector 2 provided in the center thereof. Distances 4 a,herein a black mask, is also provided, dividing the display panel 10into the respective display units 1. The display units 1 can bemultiplied to any suitable number of units 1 making up a completedisplay. Also, as shown in FIG. 3 b, each color filter 4 may include acircular reflector 2 rather than the rectangular reflectors of FIG. 3 a.The display including liquid crystal (LC) layer and lighting system (notshown) is then assembled in a portable electronic device such as amobile phone, which is illustrated in FIG. 4. It is not necessary thatthe electronic device is able to communicate in the same way as a mobilephone, but any portable electronic device where there is a need for abetter display could benefit from the invention.

FIG. 4 shows a portable electronic device 100, herein in the form of acellular phone having an antenna 14, and display 10.

Experiments performed on an 128×160 dot, 65 k color display (1/160 duty(driving condition)) have revealed that surface brightness, reflectanceand other parameters have improved compared to prior art.

The invention is not limited to pure emissive devices, but covers alsotransflective devices. The lighting system is not limited tobacklighting only, but also other system are applicable.

Thus a display unit and a portable electronic device comprising thesame, wherein two modes of operation is provided, that combines peakperformance of an emissive display with a reflective display being ableto be read without backlighting have been described. With the proposeddisplay unit according to the invention, there is no need for reflectedlight to travel through a color filter when operating in reflectivemode, without the lighting system turned on. The invention could beimplemented in both passive (STNC) and active (TFT) devices(technology), in any type of portable electronic device such asclamshell or stick mobile phone, but also in the automotive industry, orany other stationary application requiring low power consumption.

1. A display unit for a portable electronic device, comprising: asubstantially transparent display layer having a front side fordisplaying information and a rear side; a color filter layer; at leastone reflector between the color filter layer and the substantiallytransparent display layer such that no color filter is provided betweenthe at least one reflector and the substantially transparent displaylayer; and a lighting system for illuminating the substantiallytransparent display layer from the rear side via the color filter layer,the lighting system configured to be switched on or off, wherein thedisplay unit operates in an emissive mode when the lighting system isswitched on, wherein the display unit operates in a reflective and/ortransflective mode when the lighting system is switched off, and whereinthe at least one reflector is on a front side of the color filter layerfacing the display layer such that reflected light does not travelthrough a color filter when the display unit operates in the reflectivemode.
 2. A display unit according to claim 1, wherein the color filterlayer is on the rear side of the substantially transparent display layerand the front side of the color filter layer faces the substantiallytransparent display layer, and wherein the front side of the colorfilter layer includes the at least one reflector.
 3. A display unitaccording to claim 2, wherein the at least one reflector covers lessthan 50% of a total area of the rear side of the color filter layer. 4.A display unit according to claim 2, wherein the at least one reflectorcovers less than 25% of a total area of the front side of the colorfilter layer.
 5. A display unit according to claim 3, wherein the atleast one reflector is provided in a center of the front side of thecolor filter layer.
 6. A display unit according to claim 3, wherein theat least one reflector is provided adjacent to an edge of the front sideof the color filter layer.
 7. A display unit according to claim 3,wherein the at least one reflector has a rectangular shape.
 8. A displayunit according to claim 3, wherein the at least one reflector has acircular shape.
 9. A display unit according to claim 4, wherein the atleast one reflector is provided in a center of the front side of thecolor filter layer.
 10. A display unit according to claim 4, wherein theat least one reflector is provided adjacent to an edge of the front sideof the color filter layer.
 11. A display unit according to claim 4,wherein the at least one reflector has a rectangular shape.
 12. Adisplay unit according to claim 4, wherein the at least one reflectorhas a circular shape.
 13. A display unit according to claim 5, whereinthe at least one reflector has a rectangular shape.
 14. A display unitaccording to claim 5, wherein the at least one reflector has a circularshape.
 15. A display unit according to claim 6, wherein the at least onereflector has a rectangular shape.
 16. A display unit according to claim6, wherein the at least one reflector has a circular shape.
 17. Aportable electronic device comprising: at least one display unit,comprising: a substantially transparent display layer having a frontside for displaying information and a rear side; a color filter layer;at least one reflector between the color filter layer and thesubstantially transparent display layer such that no color filter isprovided between the at least one reflector and the substantiallytransparent display layer; and a lighting system for illuminating thesubstantially transparent display layer from the rear side, the lightingsystem configured to be switched on or off, wherein the display unitoperates in an emissive mode when the lighting system is switched on,wherein the display unit operates in a reflective and/or transflectivemode when the lighting system is switched off, and wherein the at leastone reflector is on a front side of the color filter layer facing a usersuch that reflected light does not travel through a color filter whenthe display unit operates in the reflective mode.
 18. A portableelectronic device according to claim 17, wherein the color filter layeris on the rear side of the substantially transparent display layer andthe front side of the color filter layer faces the substantiallytransparent display layer, and wherein the front side of the colorfilter layer includes the at least one reflector.